1. Field of the Invention
The present invention relates to a substrate processing apparatus which processes a substrate by a predetermined treatment which uses processing liquid while rotating the substrate.
2. Description of the Background Art
FIG. 1 is a vertical cross sectional view showing an example of a conventional substrate processing apparatus 101. In the substrate processing apparatus 101, a substrate W is held by a rotation stage 121 in a horizontal direction and rotated about a center axis Z, which is in a vertical direction, through a rotation shaft 122 which is connected to the rotation stage 121. In addition, to a surface of the substrate W which is rotated, processing solution, pure water, nitrogen gas and the like are supplied through a processing solution supply pipe 141 and a gas supply pipe 142.
Further, in such a substrate processing apparatus, a cover plate 131 is disposed in a faced relationship with the substrate W in order to isolate the substrate W from an external atmosphere, and the rotation stage 121 is enclosed on side by a cup 151.
Such a structure described above allows processing solution to be dropped down from the processing solution supply pipe 141, aiming at removing an oxide film or the like from the surface of the substrate W, during or immediately prior to rotation of the substrate W achieved by the rotation stage 121. Following this, pure water is supplied while rotating the substrate W so that the substrate W is cleaned, and nitrogen gas is then blown toward the substrate W from the gas supply pipe 142 so as to dry the substrate W.
FIG. 2 is a diagram of a bottom surface 131a of the cover plate 131 (hereinafter referred to "cover surface"), viewed from below, which is faced with a top surface of the substrate W. At the cover surface 131a of the cover plate 131, as the substrate W rotates in the direction or an arrow Rot, an air stream is created as indicated by arrows AR1. The air stream flows toward the center axis Z like a vortex, bearing off toward the center axis Z which is the center of rotation of the substrate W from a circumferential direction. Arrows AD indicate the directions and the strengths of the air stream at different positions. In FIG. 1, a general presentation of the air stream at the vertical cross section is given as arrows AR2.
Since the air stream flowing toward the center is created at the cover surface 131a in this manner, among drops of chemical liquid or pure water which are spattered off the substrate W after dropped on the surface of the substrate W, drops DR adhering to the cover surface 131a move toward the center as shown in FIG. 1. However, while moving toward the center, the drops DR merge into larger drops and eventually fall off onto the surface of the substrate W because of gravity. As a result, dusts and contaminants which are contained in the drops DR adhere to the substrate W, which leads to an uneven treatment of the substrate W and degrades the quality of the substrate W.